This invention relates to a chromium-nickel-silicon-manganese bearing steel alloy and products fabricated therefrom which exhibit wear resistance and cryogenic impact strength superior to, and corrosion resistance and oxidation resistance at least equivalent to, austenitic nickel cast irons. In a preferred embodiment the alloy and cast, wrought and sintered products thereof, which are substantially fully austenitic, are superior in galling resistance to austenitic nickel cast irons and to a stainless steel disclosed in U.S. Pat. No. 3,912,503 and developed by the present inventors which was hitherto considered to have outstanding galling resistance, despite the fact that the level of expensive alloying ingredients and melting cost are much lower in the steel of this invention.
International Nickel Company has sold a series of austenitic nickel cast irons for many years under the trademarks "NI-Resists" and "Ductile NI-Resists". A number of grades is available as described in "Engineering Properties and Applications of the NI-Resists and Ductile NI-Resists", published by International Nickel Co., which are covered by ASTM Specifications A437, A439 and A571. The overall ranges for "NI-Resist" alloys are up to 3.00% total carbon, 0.50% to 1.60% manganese, 1.00% to 5.00% silicon, up to 6.00% chromium, 13.5% to 36.00% nickel, up to 7.50% copper, 0.12% maximum sulfur, 0.30% maximum phosphorus, and balance iron. The "Ductile NI-Resists" are similar in composition but are treated with magnesium to convert the graphite to spheroidal form.
U.S. Pat. No. 2,165,035 discloses a steel containing from 0.2% to 0.75% carbon, 6% to 10% manganese, 3.5% to 6.5% silicon, 1.5% to 4.5% chromium, and balance iron.
U.S. Pat. No. 4,172,716 discloses a steel containing 0.2% maximum carbon, 10% maximum manganese, 6% maximum silicon, 15% to 35% chromium, 3.5% to 35% nickel, 0.5% maximum nitrogen, and balance iron.
U.S. Pat. No. 4,279,648 discloses a steel containing 0.03% maximum carbon, 10% maximum manganese, 5% to 7% silicon, 7% to 16% chromium, 10% to 19% nickel, and balance iron.
U.S. Pat. No. 3,912,503 issued to the present inventors, discloses a steel (sold under the trademark NITRONIC 60) containing from 0.001% to 0.25% carbon, 6% to 16% manganese, 2% to 7% silicon, 10% to 25% chromium, 3% to 15% nickel, 0.001% to 0.4% nitrogen, and balance iron. This steel has excellent galling resistance.
Other publications disclosing chromium-nickel-silicon bearing steels, and including varying levels of carbon and manganese, include U.S. Pat. Nos. 2,747,989; 3,839,100; 3,674,468; British Pat. No. 1,275,007 and Japanese No. J57185-958.
AISI Type 440C is a straight chromium stainless steel (about 16% to 18% chromium) considered to have excellent wear and galling resistance.
The manufacturer of "NI-Resists" alloys alleges that they are satisfactory in applications requiring corrosion resistance, wear resistance, erosion resistance, toughness and low temperature stability. Wear resistance is intended to refer to metal-to-metal rubbing parts, while erosion resistance is referred to in connection with slurries, wet steam and gases with entrained particles.
Although galling and wear may occur under similar conditions, the types of deterioration involved are not similar. Galling may best be defined as the development of a condition on a rubbing surface of one or both contacting metal parts wherein excessive friction between minute high spots on the surfaces results in localized welding of the metals at these spots. With continued surface movement, this results in the formation of even more weld junctions which eventually sever in one of the base metal surfaces. The result is a build-up of metal on one surface, usually at the end of a deep surface groove. Galling is thus associated primarily with moving metal-to-metal contact and results in sudden catastrophic failure by seizure of the metal parts.
On the other hand, wear can result from metal-to-metal contact or metal-to-non-metal contact, e.g., the abrasion of steel fabricated products by contact with hard particles, rocks or mineral deposits. Such wear is characterized by relatively uniform loss of metal from the surface after many repeated cycles, as contrasted to galling which usually is a more catastrophic failure occurring early in the expected life of the product.